The present invention relates to a motor vehicle collision sensing device and, more particularly, to a motor vehicle collision sensing device used in a safety system of the type which inflates one or more air bags in case of a collision.
Recently, there has been developed an air bag system for protecting a driver and passengers in case of a collision of motor vehicles. Such an air bag system has a collision sensing device which generates a collision signal when a collision occurs. When the collision signal is generated, an explosive is ignited so as to instantaneously inflate an air bag, thereby preventing a driver and passengers from being thrown forward. In such a system, one of the most important component parts is the collision sensor which actuates an explosive ignition circuit exactly at the time of a collision.
Various types of the collision sensors have been developed, and among them, a Rollamite type which comprises a rollspring and a roller is most typical. In this type of the collision sensor, a roller mass is rotatably supported by a fork-shaped support leaf and is normally held in abutment with a retaining member at one end of the support leaf. When collision occurs, the roller mass rolls over the surface of the support leaf and an electric contact attached to the outer surface of the cylindrically rolled portion of the support leaf is brought into contact with a stationary electric contact disposed between two legs of the support leaf, so that an ignition circuit for an explosive, such as a squib, is turned on via the closed contacts.
The free ends of the two legs of the fork-shaped support leaf are securely joined to a common connecting member which in turn is connected to a single resistor to form a breakdown detecting circuit or a diagnosis circuit.
The Rollamite type collision sensing device of the type described above does not accomplish its function properly if it is damaged. In order to eliminate this problem and to improve its reliability in operation, the diagnosis circuit mentioned above is provided which is capable of electrically warning of the damage of the collision sensor. The collision sensor of the type described above is, for example, disclosed in Japanese Laid-Open Patent Publication (KOKAI) No. 54-47244 published Apr. 13, 1979.
In the collision sensor of the type described above, the resistance of the diagnosis circuit becomes infinitely large if the (non-bifurcated) base portion and/or both the bifurcated leg portions of the fork-shaped support leaf are broken, whereby the breakdown of the collision sensor can be detected. However, if only one of the two leg portions of the support leaf is broken, electric current can flow through one of the leg portions of the support leaf so that the breakdown detecting circuit cannot perform its function. Thus, there arises the problem that breakdown or damage of the collision sensor is not perfectly detected.